1. Field of the Invention
This invention relates to a process for production of olefins, aromatic, syn-gas (hydrogen, carbon monoxide), process heat, and coke by co-feeding oxygenated compounds, such as glycerol, carbohydrates, sugar alcohols or other oxygenated biomass-derived molecules such as starches, cellulose, and hemicellulose-derived compounds) with petroleum derived feedstocks in a modified fluid catalytic cracking process.
2. Description of the Related Art
Fluid catalytic cracking (FCC) is the most widely used process for the conversion of crude oil into gasoline, olefins and other hydrocarbons. The FCC process consists of two vessels coupled together as shown in FIG. 1. In the first reactor a hot particulate catalyst is contacted with hydrocarbon feedstocks, thereby producing cracked products and spent coked catalyst. After the cracking reaction takes place the catalyst is largely deactivated by coke.
The coked catalyst is separated from the cracked products, stripped of residual oil by steam stripping and then regenerated by burning the coke from the deactivated catalyst in a regenerator. The hot catalyst is then recycled to the riser reactor for additional cracking. A variety of process configurations and catalysts have been developed for the FCC process. The heart of the FCC catalyst is a faujasite zeolite. New medium, large and extra-large pore zeolites are actively searched to achieve a higher flexibility in product distribution.
The European Commission has set a goal that by 2010, 5.75% of transportation fuels in the EU will be biofuels. Blending biofuels with petroleum based fuels will help to reduce dependence on imported crude oil, reduce emission of greenhouse gases, and improve agricultural economies. Using FCC processes for biomass conversion does not require a significant capital investment, as FCC plants are already installed in petroleum refineries. It would therefore represent a considerable advance in the state of the art if efficient methods were developed to use the FCC process to convert biomass-derived molecules into transportation fuels.
Several methods have been reported for conversion of biomass-derived molecules into liquid fuels using zeolite catalysts. Chen and Koenig in U.S. Pat. No. 4,933,283 and U.S. Pat. No. 4,549,031 (Mobil) report a process for conversion of biomass derived carbohydrates, starches and furfural into liquid hydrocarbon products, CO, and coke, by passing aqueous streams over zeolite catalysts at 500° C.[Chen, 1986 #9; Chen, 1990 #10] They observed that 40-66% of the carbon leaves the reactor as coke when xylose, glucose, starch and sucrose are fed over a ZSM-5 catalyst at 500° C.[Chen, 1986 #9] Other products formed include hydrocarbons, CO, and CO2. Mixing the aqueous-carbohydrate streams with methanol leads to lower levels of coke and higher levels of hydrocarbons being formed.
Chen et al. report the major challenge with biomass conversion to be the removal of oxygen from the biomass and enriching the hydrogen content of the hydrocarbon product. They define the effective hydrogen to carbon ratio (H/Ceff) defined in Equation 1. The H/Ceff ratio of biomass derived-oxygenated hydrocarbon compounds is lower than petroleum-derived feedstocks due to the high oxygen content of biomass-derived molecules. The H/Ceff ratio of carbohydrates, sorbitol and glycerol (all biomass-derived compounds) are 0, 1/3 and 2/3 respectively. The H/Ceff ratio of petroleum-derived feeds ranges from 2 (for liquid alkanes) to 1 (for benzene). In this respect, biomass can be viewed as a hydrogen deficient molecule when compared to petroleum-based feedstocks.
                              H          /                      C            eff                          =                              H            -                          2              ⁢              O                        -                          3              ⁢              N                        -                          2              ⁢              S                                C                                    (        1        )            where H, C, O, N and S are the moles of hydrogen, carbon, oxygen, nitrogen and sulfur respectively.
Glycerol is currently a valuable by-product of biodiesel production, which involves the transesterification of triglycerides to the corresponding methyl or ethyl esters. As biodiesel production increases, the price of glycerol is projected to drop significantly. In fact, the price of glycerol has already dropped by almost half over the last few years. [McCoy, 2005 #6] Therefore it is desirable to develop inexpensive processes for the conversion of glycerol into chemicals and fuels.
Methods for conversion of solid biomass into liquids by acid hydrolysis, pyrolysis, and liquefaction are well known [Klass, 1998 #12]. Solid materials including lignin, humic acid, and coke are byproducts of the above reaction. A wide range of products are produced from the above reactions including: cellulose, hemicellulose, lignin, polysaccharides, monosaccharides (e.g. glucose, xylose, galatose), furfural, polysaccharides, and lignin derived alcohols (coumaryl, coniferyl and sinapyl alcohols).
Bio-oils, produced by fast pyrolysis or liquefaction of biomass, are a mixture of more than 300 compounds. Bio-oils are thermally unstable, and need to be upgraded if they are to be used as fuels. Bio-oils, and bio-oil components, can be converted to more stable fuels using zeolite catalysts. [Bridgwater, 1994 #14] Reaction conditions used for the above process are temperatures from 350-500° C., atmospheric pressure, and gas hourly space velocities of around 2. The products from this reaction include hydrocarbons (aromatic, aliphatic), water-soluble organics, water, oil-soluble organics, gases (CO2, CO, light alkanes), and coke. During this process a number of reactions occur including dehydration, cracking, polymerization, deoxygenation, and aromatization. However poor hydrocarbon yields and high yields of coke generally occur under these reaction conditions, limiting the usefulness of zeolite upgrading.
Bakhshi and co-workers studied zeolite upgrading of wood derived fast-pyrolysis bio-oils and observed that between 30-40 wt % of the bio-oil formed coke or char. (Sharma and Bakhshi 1993; Katikaneni, Adjaye et al. 1995; Adjaye, Katikaneni et al. 1996) The ZSM-5 catalyst produced the highest amount (34 wt % of feed) of liquid organic products of any catalyst tested. The products in the organic carbon were mostly aromatics for ZSM-5, and aliphatics for SiO2—Al2O3. Gaseous products include CO2, CO, light alkanes, and light olefins. Bio-oils are thermally unstable and thermal cracking reactions occur during zeolite upgrading. Bakhshi and co-workers also developed a two-reactor process, where only thermal reactions occur in the first empty reactor, and catalytic reactions occur in the second reactor that contains the catalyst. (Srinivas, Dalai et al. 2000) The reported advantage of the two-reactor system is that it improved catalyst life by reducing the amount of coke deposited on the catalyst.
The transformation of model bio-oil compounds, including alcohols, phenols, aldehydes, ketones, acids, and mixtures, have been studied over HZSM-5 catalysts. (Gayubo, Aguayo et al. 2004; Gayubo, Aguayo et al. 2004; Gayubo, Aguayo et al. 2005) Alcohols were converted into olefins at temperatures around 200° C., then to higher olefins at 250° C., followed by paraffins and a small proportion of aromatics at 350° C. (Gayubo, Aguayo et al. 2004) Phenol has a low reactivity on HZSM-5 and only produces small amounts of propylene and butanes. 2-Methoxyphenol also has a low reactivity to hydrocarbons and thermally decomposes, generating coke. Acetaldehyde had a low reactivity on ZSM-5 catalysts, and it also underwent thermal decomposition leading to coking problems. (Gayubo, Aguayo et al. 2004) Acetone, which is less reactive than alcohols, converts into C5+ olefins at temperatures above 350° C. These olefins are then converted into C5+ paraffins, aromatics and light alkenes. Acetic acid is first converted to acetone, and that then reacts as above. Products from zeolite upgrading of acetic acid and acetone give considerably more coke than products from alcohol feedstocks. Thus, different molecules in the bio-oils have a significant difference in reactivity and coke formation rates.
Catalytic cracking of vegetable oil can be used to produce a liquid fuel that contains linear and cyclic paraffins, olefins, aldehydes, ketones, and carboxylic acids. The cracking of vegetable oils has been studied since 1921, and pyrolysis products of vegetable oils were used as a fuel during the 1st and 2nd World Wars. Both homogeneous and heterogeneous reactions are occurring during catalytic cracking of vegetable oils. The pyrolysis reaction can be done with or without a catalyst, and a number of catalysts have been tested including HZSM-5, β-zeolite, and USY.60,61 Twaiq et al. used a ZSM-5 catalyst to produce yields of 28, 9, and 5% gasoline, kerosene, and diesel fuel respectively from a Palm oil feed. Lima et al. claim that pyrolysis products with a ZSM-5 catalyst and soybean and palm oil feedstock, have fuel properties similar to Brazilian Diesel Fuel.